Electric circuit breaker wherein the operation of separable arcing contacts is dependent on the magnitude of current in the main contacts



FOR NWALT 3,249,729 ELECTRIC CIRCUIT BREAKER WHEREIN THE OPERATION OF SEPARABLE May 3, 1966 M. B.

ARCING CONTACTS IS DEPENDENT ON THE MAGNITUDE OF CURRENT IN THE MAIN CONTACTS 2 Sheets-Sheet 1 Filed 001. 1a, 1963 INVENTOR MAX 5. FbR/VWALT, B) M 1 W Q4.

ATTORNEY.

y 3, 1966 M. B. FORNWALT 3,

ELECTRIC CIRCUIT BREAKER WHEREIN THE OPERATION OF SEPARABLE ARCING CONTACTS IS DEPENDENT ON THE MAGNITUDE OF CURRENT IN THE MAIN CONTACTS ATTORNEY.

3,249,729 Patented May 3, 1966 3,249,729 7 ELECTRIC CIRCUIT BREAKER WHEREIN THE OPERATION OF SEPARABLE ARCING CON- TACTS IS DEPENDENT ON THE MAGNITUDE OF CURRENT IN THE MAIN CONTACTS Max B. Fornwalt, S ringfield, Pa., assignor to General Electric Company, a corporation of New York Filed Oct 18 1963, Ser; No.- 317,213 12 Claims. (CL 200-166) This invention relates to electric circuit breakers or interrupters, and more particularly it relates to an improved electric contact structure for low voltage power circuit breakers.

' Designers of low voltage (e. g., 600 volts) electric circuit breakers have perennially sought ways of improving breaker performance while minimizing size and manufacturing expense. The design objectives are well known. It is generally recognized that circuit breakers of good design have to be able to aptly perform a number of.

primary functions: conduct rated current continuously, within prescribed limits of temperature rise; safely open full load current at rated voltage, and also safely interrupt fault or short circuit currentwhose magnitude is likely to be many times greater than that of full load current; selectively endure short circuit conditions without opening for predetermined short intervals of time; and successfully competing demands are involved. For example, a preferred design for main contacts, in a 6Q0-volt A.-C circuit breaker that is capable of conductingmore than 60f) amperes continuously, is not compatible with the demands of a high interrupting capacity (e.g. 50,600 amperes), and

therefore parallel auxiliary or arcing contactsof good arc-erosion resistant material are needed. But the addition of arcing contacts can create new problems with respect to the close and latch duty of the breaker. As a result, a contact making and breaking sequence is desirable wherein the arcing contacts of a circuit breaker are the last to close as well as the last to open, and somewhat complex mechanisms have heretofore been developed in the art for obtaining this end. K

Power circuit breakers are often used in lowvoltage electric distribution systems where a plurality of coordinated, sequentially operative protective means are employed. In such a selective trip? setting, the short time capability of the breaker is particularly important. This attribute of the breaker is a measure of its ability to successfully remain closed for a predetermined interval of time while conducting short circuit or fault current. During the predetermined interval, in -a selective trip; system, opening of the breaker is deliberately delayed in order to allow time for protective means more remote from the source to preferentially clear the fault.

Whenever the primary conducting parts of a breaker are subjected to shortcircuit currents, relatively high electrodynamic forces (proportional to the current magnitude .squared) are exerted thereon, and there is a tendency under fault conditions for the breaker contacts to separate or open. If the contacts separate prematurely, during the short time interval following the inc-idence of a fault before the breaker opening mechanism is duly actuated, un-

propitious arcing and severe contact erosion or welding can occur, to the detrimentof breaker operability and life. To overcome this problem, those working in the art have heretofore suggested contact designs in which increased ,electrodynamic forces that attend a fault are utilized to I increase contact pressure and to assist in holding the con- Accordingly it is a general objective of the present invention to provide improved contact means for a low voltage power circuit breaker having, in optimum combination, a high interrupting capacity, good short time capability, a relatively long life, and a compact, easily operated structure.

Another object of my invention is to provide a relatively simple contact structure including both main and arcing contact means wherein the arcing contact means never close before the main contact means.

Still another object of the invention is the provision of an improved circuit breaker having relatively high interrupting and short time capabilities and requiring a relatively low amount of energy to close the breaker on either an unloaded circuit or a faulted circuit.

It is a more specific object of my invention to modify the contact structure design disclosed and claimed in US. Patent No. 3,073,936 granted toL. L. Baird on January 15, 1963, so as to significantly improve its performance capabilities without changing its overall size.

In carrying out my invention in one form, an electric circuit breaker is provided with a pair of separable main contact means for conducting current, when engaged, in an electric power circuit, and the breaker additionally includes two arcing contact means connected, when eng'aged, in shunt with the main contact means. Operating means is provided for moving the main contact means into and out of circuit making engagement with each other and, concurrently, for moving one of the arcing con-tact means toward and away from a position of proximity to the other. I arrange this structure so that the two arcing contact means remain separated during movement of the main contact means into mutual engagement, and so that interengagement of the arcing contact means is subsequently effected in response to an appreciable increase in the magnitude of current conducted by the main contact means, independently of operation of the operating means. The arcing contact means are further arranged to be interengaged electrically after the main contact means have separated on opening movement by the operating means.

Since the initial interengagement of the arcing contact means of a circuit breaker constructed in the abovesummarizedmanner is dependent on current being conducted in the main contact means, the arcing contact means will not touch duringa closing operation until after the main contact means have engaged and are conducting appreciable current, by which time the closing operation is nearly complete. This minimizes the forces resisting closing, and only a reasonable amount of energy is needed to ensure closing on a faulted circuit without stalling. On the other hand, whenever the breaker is closed and subjected to short time faults or severe interrupting duty, the arcing contact means are interengaged and will contribute on their part to superior breaker performance. In one aspect of the invention, the short time capability of my contact structure is even further improved by providing means responsive to the conduction of current by the interengaged arcing contacts for augmenting contact pressure thefebetween and preventing untimely separation thereof.

My invention will be better understood and its various objects and advantages will be more fully appreciated from the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a side elevation of a circuit breaker contact structure embodyinga preferred form of my invention,

with the movable contact member of the contact structure shown in its open circuit position;

FIG. 2 is a front elevation of the contact structure illustrated in FIG. 1;

FIG. 3 taken along lines 44; and

FIG. 5 is a partial plan sectional view of the structure of FIG. 3 along lines 55, the movable contact member having been moved to an intermediate position early in the breaker opening operation.

Referring now to FIGS. 1 and 2, I have shown an electric circuit breaker or interrupter comprising a base member 11, a relatively stationary contact member 12 mounted on the base, an electroconductive bracket 13 mounted on the base in spaced relation to the stationary contact member, a movable contact member 14 pivotally supported by bracket 13 and disposed in cooperative relationship with the stationary contact member 12, and actuating means such as a crossbar 15 coupled to the movable contact member 14 for moving this member into -and out of circuit making engagement with the stationary contact member 12. The components 12, 13, and 14 comprise the contact structure of one pole unit of an alternating or direct'current circuit breaker, and other similar pole units (not shown) can be mounted for gang operation on the base member 11 adjacent to the pole unit that has been illustrated in FIGS. 1 and 2.

The base member 11, preferably comprising a rigid sheet of electric insulating material formed in the manner taught by Baird in his above-cited patent, supports the current-conducting studs of the breaker, the supporting bracket 13, and the other breaker parts connected thereto. The bracket 13, to which the movable contact 14 is connected, is connected in turn to an outgoing conductor 16 by way of current sensing means of an overcurrent trip device shown symbolically at 17 in FIG. 1. An upper breaker stud 18 of the breaker, to which the relatively stationary contact member 12 is connected, ex-

tends rearwardly therefrom through an appropriate aperture in the bottom of a channel-shaped section of base 11, as can be seen in FIG. 1, and a conductor 19 is shown connected to the stud 18. The contact members 14 and 12, by movement into and out of engagement with each other, are adapted to close and to open, respectively, an

electric power circuit represented by the two conductors 16 and 19. This circuit may be connected in a 600-volt A.-C. electric power system having the capacity to supply as much as 50,000 amperes short-circuit current at 600 volts, and a breaker having my contact structure (which is designed to conduct more than 600 amperes continuously without exceeding permissible limits of temperature rise) can successfully interrupt this maximum shortcircuit current. Of course the circuit breaker may be applied in any electric power system to which its capabilities are suited, and the above-mentioned ratings have been set forth only for the purpose of illustrating one range of magnitudes specifically contemplated.

The upper stud 18 of the circuit breaker is secured to base 11 by a generally L-shaped angle 20 illustrated in FIG. 1. The angle 20 is disposed above the stud 18 and is fastened thereto by three copper rivets 21 or the like. The upstanding limb of the angle is provided with a threaded stud 22 by means of which it is secured to the base 11 as shown. The forward end of the breaker stud 18, in the preferred embodiment of my invention, provides support for one part of the stationary contact member 12, this part being identified as the relatively staengagement with all of the cooperating contact surfaces 25, and further rearward movement of the surto be described soon hereinafter.

tionary main contact means. This means itself comprises a plurality of electrically parallel, elongated contact elements or fingers 24 which have been constructed and arranged in the manner disclosed and claimed by C. H. Titus in his Patent 3,033,964 granted on May 8, 1962. The Titus patent can be referred to for a more detailed showing and explanation of this part of my contact structure, which part will now be only briefly described.

The forward end of the breaker stud 18 is divided into two horizontally diverging branches, thereby having in plan view a generally Y shaped appearance, and each of the elongated elements or fingers 24 is supported for pivotal movement on the outer end of one of these branches. For this purpose, the outer end of each diverging branch is provided with a generally cylindrical bearing surface which provides a fulcrum for a set of two parallel contact fingers, and the pivotal connection between each finger and the breaker stud forms a current-conducting joint. As can be clearly seen in FIGS. 2 and 3, the contact fingers 24 are arranged in vertically adjacent pairs, all being electrically interconnected by virtue of the common stud 18. The fingers of each pair are respectively supported on opposite bearing surfaces in opposing relationship with respect to each other, with the opposing fingers of each pair being pivotally movable in a common horizontal plane. The opposing or inner ends of the contact fingers of each pair move in separate, relatively short *arcuate paths. The opposing ends of the fingers are respectively provided with generally flat, complementary butt contact surfaces 25 normally disposed in a common vertical plane as viewed in FIGS. 1 and 2.

The inner end of each contact finger 24 has an extension 26 disposed to engage a common stop 27 (see FIGS. 4 and 5) for determining the limit of the arcuate movement of the contact surface 25 in one direction.

The stop 27 comprises a pin vertically disposed intermediate the divergent branches of the breaker stud 18 and fixedly-mounted at upper and lower ends by means The outer end 28 of each contact finger 24 has suitable spring means associated therewith, for example a tension spring 29 which, as shown in FIG. 1, is anchored to a fixed member such as pro'vided'by 'a laterally extending lug 30 of the supporting angle 20. Thus, spring means 29 establishes a biasing torque in the contact finger 24 tending to move the contact surface 25 along an arcuate path in a forward direction away from the base 11, and .as is best seen in FIG. 5, such movement by the finger is limited by stop pin 27. As a result of this arrangement, relatively limited deflection or yielding of each contact finger in a rearward direction is permitted.

The biasing torque of each spring 29 is opposed and overcome, and each contact finger 24 of the relatively stationary contact member 12 is tilted slightly on its ful crum, bythe action of the movable contact member 14.

As will be fully explained below, the movable contact member 14 includes a pair of electrically parallel arms 38 and 40 respectively provided with butt contact surfaces 43 which move in parallel planes disposed approximately perpendicular to the planes defined by the parallel arcuate paths of the contact surfaces 25 of each set of adjacent fingers 24. The operating means 15 of the breaker provides actuating force for moving each contact surface 43 of member 14 into and out of circuitmaking abutting engagement with adjacent contact surfaces 25 of two parallel contact fingers. During a circuit making operation, the contact surfaces43 are jointly carried rearwardly from their open circuit position (FIGS. 1 and 2) into substantially simultaneous abutting faces 43 from a position of initial engagement to their final closed circuit position (FIGS. 3 and 4) will force spring means 29 tostretchas the yieldably supported contact fingers; 24 tilt on their fulcrums. In this manner conventional contact wiping action is obtained.

In FIGS. 1 and 2 it can be seen that the electroconductive bracket 13 for supporting the movable contact member 14 is mounted on the breaker base 11 by means of a pair of suitable bolts 31 or the like. The bracket 13 includes a pair of spaced-apart upstanding lugs 32 and 33 projecting in front of the base 11. A removable pivot pin 34 is supported by the lugs 32 and 33, the axis of the pivot pin extending in a horizontal direction generally parallel to the plane of the base as viewed in the drawings. The pivot pin 34, which passes through both of the lugs 32 and 33 and protrudes from their outwardly facing sides, respectively, is retained in place by 'a releasable clamp 35 connected to the pin between the lugs. The outwardly facing side of each lug is provided with a substantially flat slide surface 36. Disposed adjacent to the slide surface 36 of lug 32 and rotatably mounted on pivot pin 34 is one end 37 of an elongated contact arm 38; and disposed adjacent to the slide surface 36 of lug 33 and rotatably mounted on the pivot pin 34 is one end 39 of another elongated contact arm 40. The arms 38 and 40 are arranged in side by side spaced-apart relation for joint pivotal movement on the pin 34 during breaker closing and opening operations. They comprise the movable contact member 14 of my contact structure.

The connection between each movable contact arm 38, 40 and the electroconductive bracket 13 is anranged to provide three separate but electrically parallel current-conducting joints. The first such joint is provided by the bearing surfaces between the arm and the pivot pin 34 on whichit rotates, that is, between 34 and the periphery of a hole which is provided in the supported end of the arm to accommodate the pin 34. Another current-conducting joint is obtained'by providing the supported end 37, 39 of each movablecontact arm 38, 40

with .a pertaining slide surface 41 on its relatively broad inner side, i.e., on the side of thearm facing the companion arm.

Each slide surface 41 is disposed generally parallel to the adjoining slide surface 36 of the associated lug 32, 33 of the supporting bracket 13. Both slide surfaces 36 and 41 are disposed substantially perpendicular to the axis of the pivot pin 34, which corresponds to the axis of rotation of the movable arms 38 and 40. In accordance with the teachings of Patent 2,962,573 granted to T. I. Scully on November 29, 1960, the slide surface 41 includes a raised section whose crest is oriented at approximately a right angle with respect to the longitudinal centerline of the contact arm and is intersected by the pivot pin. The crest of the raised section of slide surface 41 is contiguous with slide surface 36 of bracket 13, and pivotal movement of the arm on pin 34 causes the crest to slide over the surface 36. The contiguous portions of the slide surfaces 36 and 41 define a line contact which provides the second current-conducting joint between each movable contact arm and the supporting bracket.

Contact pressure at the joint formed by the contiguous slide surfaces is maintained by means of an electroconductive spring member 42 which preferably comprises a U-shaped spring clip, the upstanding legs of the clip being split for respectively bearing against the relatively broad outer sides of each contact arm 38, 40 at points disposed on opposite sides of the pivot pin. 34. The clip 42 is secured to the bracket 13, and since it also is in engagement with each movable contact arm it provides the third current-conducting joint. In addition, it supplies a force which maintains contact pressure between the contiguous slide surfaces 36 and 41. This force is supplemented by an electrodynamic force whenever the movable contact member 14 is conducting current. Since the parallel arms 38 and 40 pass current in the same direction, a magnetic force of attraction is established tending to reduce the spacing between their supported ends 37 and 39, whereby additional contact pressure is exerted at the contiguous slide surfaces 36 and 41, the magnitude of this force being proportional to the square of the current magnitude.

The diameter of the hole in the movable contact arms through which the pivot 34 passes is made slightly greater than the diameter of the pin, whereby the movable contact member 14 is loosely mounted on the bracket 13. This arrangement permits the arms 38 and 40 to rock on the pivot pin 34. The crest of the raised section of slide surface 41 provides a fulcrum for the rocking movement of each arm. This arrangement allows for a certain degree of misalignment of the various parts and a liberal manufacturing tolerance without adversely afi'ecting the positiveness of the electric contact between the movable arms and the supporting bracket. v

Joint pivotal movement of the arms '38 and 40 on the pivot pin 34 will cause each of the corresponding free ends of these arms to follow a major course of movement which is along a predetermined arcuate path. The respective arcuate paths of these free ends define parallel vertical planes intersecting at approximately right angles the horizontal planes of movement of the respective pairs of relatively stationary contact fingers 24. Each of the arms 38 and 40 carries, in the vicinity of its free end, an elongated butt contact surface 43 generally tranverse its plane of movement.

The respective surfaces 43, which form the movable main contact means of my contact structure, are disposed for separable engagement with the previously described butt contact surfaces 25 of the fingers 24 of the relatively stationary contact member 12. Each contact surface 43 preferably is generally cylindrically shaped, and it defines with the abutting surface 25 of each cooperating finger 24, when the movable contact member 14 is in its closed circuit position, a relatively narrow area of contact engageinent. Two different stationary contact fingers have been provided for each movable contact arm, whereby four separate points of circuit-closing engagement are available between these separable main contact means. This relatively simple and compact arrangement, which follows the teachings of the above-cited Baird patent, permits the mass of the moving parts to be minimized, thus permitting higher operating speeds while lessening impact stresses and thereby prolonging the mechanical life of the contact structure.

In order jointly to move the arms 38 and 40 of the movable contact member 14 between open and closed circuit positions, a cylindrical impelling shaft 45, best seen in FIG. 2 is extended transversely through a midsection of each arm. Opposite ends 46 of the shaft 45 are attached to a generally U-shaped connecting link 47 which is securely fastened to the cross bar 15. Each leg of the connecting link 47 has an extension which, as is clearly seen in FIG. 1, is connected to the pivot pin 34. Thus, the crossbar 15 is supported for pivotal movement on pin 34. The end portions 46 of the impellin'g shaft 45 have been made hexagonal in cross section and eccentric with respect to the cylindrical body of the shaft, and they are positively but resiliently locked to theconnecting link 47 as shown, whereby the shaft 45 can be rotated to any one of six different angular positions. This enables the fully closed position of the movable contact member 14 to be predetermined accurately, regardless of liberal manufacturing tolerances, and the desired amount of contact wipe can be precisely obtained. p

The impellingshaft 45 is driven by the cross bar 15, to which it is coupled as explained above. The crossbar in turn is appropriately moved about its pivot, between first and second relatively fixed positions, by a breaker operating mechanism 48 connected thereto. The operating mechanism 48 of the circuit breaker is symbolically represented in FIG. 1. A detail showing of this mechanism and of the means for connecting it to the crossbar 15 is be- 7 lieved unnecessary for a complete understanding of the present invention.

Those skilled in the art will appreciate that there is available in the art a numberof different constructions of a mechanism 48 suitable for the present purposes, such as, for example, the operating mechanism that is the subject matter of Patent 2,961,509, Baird et al. Such a mechanism typically comprises closing and opening springs; closing means for actuating the springs so as to move the movable contact member 14 of the breaker from open to closed circuit positions; latching means for releasably holding the mechanism in its closed disposition; a rotatable trip shaft for releasing the latching means; and means for rotating the trip shaft and hence actuating the mechanism so as to move the member 14 from closed to open circuit positions. The last-mentioned means, in the operating mechanism represented in FIG. 1, includes a lever or paddle member 49 which is struck and tilted (thereby unlatching the mechanism 48 and initiating an opening operation thereof) by an element 50 of the overcurrent trip device 17 in response to the conduction of more than a predetermined amount of current by the cooperating contact members 14 and 12.

The impelling shaft 45 is fitted relatively loosely in holes in the midsections of the movable arms 38 and 40 through which it extends, whereby each arm can slide somewhat on shaft 45 while rocking on the pivot pin 34. Thus the free end of each arm can undergo minor movement in a transverse direction with respect to the plane defined by the arcuate path of movement of its butt contact surface 43 during circuit closing and opening operations. This lateral movement of the arms is controlled by resilient means associated therewith. As is shown in FIG. 2, the resilient means preferably comprises a helical compression spring 51 disposed on the impelling shaft 45 intermediate the arms 38 and 40. The spring 51 applies oppositely directed transverse forces to the pair of arms and establishes in each arm a relatively weak biasing torque-with respect to the pivot provided by the line contact at'the joint formed by the contiguous slide surfaces 36 and Y41. This biasing torque is in a direction tending to spread apart the contact arms. Such movement of each arm is stopped by a bushing 52 disposed on the shaft 45 adjacent to the midsection of the arm, between the outboard side thereof and a retaining ring or the like.

During circuit making action of the contact structure, the shaft 45 impels both arms of the movable contact member 14 pivotally on pivot pin 34, and the butt contact surfaces 43 are carried into abutting engagement with the respective butt contact surfaces 25 of the relatively stationary contact fingers 24. As the movable contact member 14 continues itspivotal movement from this position of initial engagement toward its fully closed position, each contact finger 24 is tilted in opposition to the biasing torque of spring 29. The arrangement is such that a transverse force is supplied to the contact surface 43 by contact surface 25 as the associated finger 24 is so deflected. Due to the resilient means 51, the movable contact arm yields to this transverse force and the contact surface 43 is able to move laterally while following the arcuate path-of surface 25. As a result, the relative movement between the cooperating butt contact surfaces 25 and 43 is reduced, thereby reducing the amount of friction between the interengaging main contact means and improving the performance of the contact structure. Such an arrangement is in accordance with the teachings of Patent 2,938,986, Baskerville et aL, granted on May 31, 1960.

The construction and operation of the main contact means so far described conform in essence to that of the compact contact structure disclosed by Baird in his prethe illustrated circuit breaker can safely carry 600 amperes continuously at 600 volts A.-C. without exceeding predetermined temperature rise limits. And by providing a suitable arc chute in association with this contact means (for which see the Baird patent), the breaker can reliably interrupt short circuit current of substantially higher magnitude. However, if this contact means were to be called upon to interrupt current of a magnitude exceeding that'for which Bairds structure was designed, the relatively high-conductivity contact material would be subject to such severe electric arcing that it would be badly eroded, to the serious detriment of breaker life and performance. I have discovered that the interrupting capacity of the basic Baird contact design, and coincidentally its short time rating, can be more than doubed without increasing breaker size by a fairly simple modification thereof, and this modification will now be de scribed.

In accordance with my invention, the arms 38 and 40 comprising the movable contact member 14 of the illustrated contact structure are respectively provided at their free ends with special contact tips or jaws 54 and 56 of relatively high arc-erosion resistant material. The tips 54 and 56, which move in parallel spaced-apart joint relation during opening and closing movement of the member 14, respectively carry slide contact surfaces 55 and 57 generally parallel totheir planes of movement. The slide surfaces 55 and 57 of the contact tips 54 and 56, forming the movable arcing contact means of my invention, are disposed facing one another, and so long as the member 14 is open, the spring 51 described hereinbefore will yieldably maintain a predetermined maximum spacing between these surfaces.

The relatively stationary contact member 12 of my contact structure includes arcing contact means positioned in cooperative relationship with the movable arcing contact means just described. As is best seen in FIG. 1, the stationary arcing contact means includes a protuberant part or blade 58 mounted bove the main contact fingers 24. FIG. 2 revels that the protuberant part 58 is disposed on a bisector' of the opposing contact fingers, and therefore it projects centrally inbetween the contact tips 54 and 56 of the arms 38 and 40 when the movable contact member 14 is closed. An electroconductive supporting member 59 connects the part 58 to the bottom surface of the upper breaker stud 18 in parallel with the fingers 24.

part 58 is firmly anchored to this flange by brazing or other suitable means. The flange 60 is secured to the angle 20 by a pair of rivets 61 that are disposed in flanged sleeves 62 of insulating material, and a piece of rigid electric insulation 63 has been sandwiched between flange 60 and angle 20 to separate the flange from the top sur face of the stud 18. The flange 60 is provided with tapped holes to anchor a pair of bolts 64 countersunk in the footing of an arc runner 65 that extends upwardly from the part 58, as is shown in FIGS. 1 and 2. The supporting member 59 also has a downturned flange 66 that is 10- cated'adjacent to the breaker base 11 below the channelshaped section through which the stud 18 extends. This flange has a pair of tapped holes, and it is secured to the insulating base member 11 by appropriate bolts 67' as shown. v

The respective flanges 60 and 66 of the supporting member 59 are joined'by two parallel, spaced-apart legs or conductors 68 disposed on opposite sides of the free ends of the movable contact arms 38 and 40. For reasons that will soon be apparent, the vertical sections of the parallel legs 68 of the member 59 have been offset frontwardly, with respect to the breaker base 11, so as to be positioned in side by side close alignment with the arms 38 and 40 while the movable contact member 14 is in its closed circuit position. A-sis best seenin FIG. 4, the lower flange 66 of member 59 base rearwardly bent extension 69 disposed immediately below the bottom surface of the breaker stud 18 to which it is conductively fastened by means of the copper rivets 21, and the extension 69 is provided with a forward lip 70 for mounting, in conjunction with the insulating piece 63 spaced thereabove,

the stop pin 27 described hereinbefore.

of. Whenever the contact surfaces 25 of the main con tact fingers 24 are engaged by the associated main contact surfaces 43 carried by the parallel arms 38 and 40 of the movable contact member 14, the slide surfaces 71 and 73 of the part 58 are respectively adjacent to the facing slide surfaces 55 and 57 on the contact tips 54 and 56 of the arms. Slide contact surface 71 is therefore adapted to be separably engaged by slide contact surface 55, :and slide contact surface 73 is adapted to be separably engaged by slide contact surface 57. However, in accordance with my invention, these cooperating surfaces remain separated and will not touch each other on movement of member 14 to its closed circuit position until after the interengaging main contactmeans conduct more than a predetermined amount of circuit current.- Thls has been accomplished inthe preferred embodiment of the invention by making the breadth of the protuberant part 58 smaller than the length of the gap separating the slide surfaces 55 and 57 when no current is being conducted, whereby the arms 38 and 40 must be moved laterally toward one another in order to effect interengagement of the respectively adjacent slide contact surfaces.

Such lateral movement of the arms 38 and 40 is effected by the electrodynamic forces of attraction acting on them in response to their parallel conduction of current of more than a predetermined amount. LThe contact structure preferably is arranged so that said predetermined amount of current is many times greater than full load current and yet is substantially less than expectable magnitudes of current under short circuit conditions. It will now be apparent that when the movable and relatively stationary members 14 and 12 of my contact structure conduct short circuit current, the parallel arms 38 and 40 experience electromagnetic forces that cause the slide contact surfaces 55 and 57 to move into engagement with the slide contact surfaces 71 and 73, respectively, thereby shunting the interengaged main contact means. Subsequent opening movement of the contact member 14 by the operating member 15 results in the main contact surfaces 43 and 25 being disengaged before the now engaged slide contact surfaces separate, as is indicated in FIG. 5. Hence the slide contact surfaces are the last opened, and any arcing that occurs will take place between the special contact tips 54, 56 and the protuberant part 58, as is shown by way of example at 74 in FIG. 1.

From the foregoing detailed descriptionof the structure of my invention,- its mode of operation may now be readily followed. The contactstructure is shown in its open circuit disposition in FIGS. 1 and 2. The movable contact member 14 is actuated by the crossbar 15, in response to a closing operation of the breaker mechanism 48, so as to move the main contact surfaces 43 into circuit making engagement with the cooperating surfaces 25 of the relatively stationary cont-act member 12 while concurrently moving the movable slide contact surfaces 55 and 57 toward positions of proximity to the stationary slide contact surfaces 71 and 73 on opposite sides of the protuberant part 58. The cooperating slide contact surfaces are adjacent to but not touching each other when the main contacts initially engage as the movable contact member 14 approaches its fully closed position near the conclusion of the closing movement.

- FIGS. 3 and 4 show the contact structure with the movable cont-act member in its closed circuit position. While the interengaged contact surfaces 25 and 43 and the parallel arms '38 and 40 can now conduct circuit current, the slide contact surfaces 55, 57 will remain separated from the respectively adjacent 'slide contact surfaces 71, 73 so long as the amount of current being conducted is not abnormally high. Under normal conditions there is in; sufficient electrodynamic attraction between the arms 38 and 40 to overcome the bias spring 51 that is urging the arms apart (see FIG. 2). I

In substantially instantaneous response to the occurrence of a short circuit in the electric power circuit being supplied via the illustrated contact structure, theforces of mutual attraction acting on the arms 38 and 40 increase substantially, and the arms move laterally toward one another to carry the movable slide contact surfaces 55 and 57 into tight engagement with the cooperating surfaces 71 and 73, respectively. This engagement effected independently of operation of themechanism 48 and the crossbar 15 and before the operating means, due to inertia and friction, can even begin opening movement of the movable member 14 in response to actuation by the meteorrent trip device 17. The direction of the resulting contact pressure between the interengaging slide contact surfaces is perpendicular to the direction of opening movement of member 14, and the more severe the short circuit, the greater this pressure. The contact pressure is further augmented by an electrodynamic force of repulsion exerted on each of the arms 38 and 40 as a result of the oppositely-directed flow of current through the respectively adjacent leg 68 of the supporting member 59. Whatever current is flowing through the interengaged slide contact surfaces also flows through the parallel legs 68 of member 59, which member interconnects the protuberant part of the stationary contact member and the breaker stud 18, and the vertical section of each leg forms with the nearest arm 38, 40 part of a series loop-shaped current conducting circuit that tends to expand with increasing current magnitude. Since each of the legs 68 is located on the outboard side of one of the movable arms 38 and 40, the loop-extension tendency results in both arms being urged laterally against the centrally disposed protuberant part 58, thereby increasing contact pressure between the associated slide contact surfaces.

The above-described construction and operation of the slide contact surfaces have produced significant improvements in the performance capabilities of the basic Baird contact design. Shorft time capabilities and interrupting capacity have both been substantially increased. Furthermore, a higher continuous current rating is possible.

My contact structure performs satisfactorily, without untimely opening or harmful arcing, when subjected to relatively high short circuit currents for a predetermined short interval of time. Under such conditions, the slide contact surfaces 55, 57 move into high-pressure clamping engagement with the cooperating surfaces 71 and 73. Any attendant reduction of contact pressure at the abutting main contact surfaces 43 and 25 is not accompanied by harmful arcing and contact contamination there, because the voltage gradient between these surfaces is repressed by the interengaged slide contact surfaces connected in shunt therewith. Note that the greater the amount of current shunted by the slide contact surfaces, the higher the contact pressure therebetween and hence the lower the contact resistance.

On subsequent opening movement of the movable contactmember 14 by the crossbar 15 in response to delayed actuation of the breaker mechanism 48 by the overcurr'erit trip device 17, the main contact surfaces 43 move entirely out of engagement with the associated surfaces 25 of the relatively stationary Contact member 12, and the cooperating slide contact surfaces separate later. FIG. 5 shows my contact structure in an intermediate disposition during an opening operation, after 43 and 25 have separated but before the contact tips 54 and 56 of the movable contact arms 38 and 40* have been moved far enough to disengage the stationary protuberant part 58-. When the slide contact surfaces later separate, an arc 74 may be drawn between one of the contact tips of the movable arms and the protuberant part 58, and therefore both tips and protuberant part have been designed to withstand arcing without harmful elfects. Note that because the cooperating slide contact surfaces are normally separated and do not conduct load current, they need not have the high conductivity that is required of the main contact means, and they are conveniently made of high arcerosion resistant material. The arcing contact tips 54 and 56 are so located that they provide a target for the arc, thereby protecting the more vulnerable contact surfaces 43 even if an arc is initiated there on interrupting load current. Ionized gases that are generated by any arcing at the main contacts will immediately cause an electric breakdown between the then separated contact tips 54,

' '56 and part 58. This materially enhances contact life.

Furthermore, my invention makes it possible to use main contact material of higher conductivity than is used in the prior art Baird design, whereby its continuous current 'rating can be increased or, given the same current rating, its temperature rise reduced.

, During the predetermined time interval following the incidence of a short circuit in a selective trip system, when opening of the breaker is deliberately delayed, the fault may be removed or preferentially cleared by downstream protective means. Although circuit current then returns to normal, it is possible for the contact tips 54 and 56 to remain in engagement with the protuberant part 58 of the arcing'contact means, the compression spring 51 being too weak to spread the movable arms 38 and 40 to their FIG. 3 position against the transverse force of the interengaged main contact surfaces 43 and 25. In this event the performance capabilities of my contact structure are not impaired.

Those skilled in the art will appreciate that in practice 'the abutting contact surfaces 25 and 43 of the illustrated contact structure could actually comprise intermediate contacts shunting additional, higher current mlain contact surfaces (not shown). In this setting the surfaces 25 and 43 would be designed to normally withstand electric arcs, and the slide contact surfaces 55, 57 and 71, 73 would serve as auxiliary arcing contacts that are effective under the most severe interrupting conditions.

An important aspect of the operation of my contact structure is, the arrangement whereby the cooperating slide contact surfaces do not touch each other during the breaker closing operation before the main contact surfaces initially engage. This minimizes the frictional and electrodynamic forces that oppose the closing force applied to the movable contact member 14, and it enables a highperformance contact structure to be closed by a relatively small and lightweight breaker mechanism, whereby contact wear is minimized and operating life enhanced. If the electric power circuit to which the breaker is connected is unloadedor only normally loaded prior to closing the breaker, the movable slide contact surfaces 55, 57 will remain separated from the associated stationary surfaces 71, 73-throughout the entire closing operation, {whereby no frictional resistance to closing is contributed by these cooperating surfaces.

If, alternatively, the electric power circuit has a preexisting fault or short circuit at the time of breaker closing, the cooperating slide contact surfaces will not touch until the main contact surfaces 43 and 25 interengage and the short circuit current conducted thereby has time to attain the predetermined magniture required to effect lateral movement of the electrically parallel arms 38 and 40 against the opposing force of the spring 51. I But by this time the movable contact member 14 will have been moved into or almost into its final closed circuit position. Under such conditions, the frictional and electrodynamic resistance to closing is substantially less than if the'cooperating slide contact surfaces had touched prior to the initial engagement of the main contact surfaces; In fact, without this feature ofmy invention thebreaker could fail to close on short circuits of the contemplated'severity,

since the resulting seizing or clamping action of the contact tips of the movable arms 38 and 40 against the protuberant part 58 might stall the closing mechanism.

While I have shown and described a preferred form of my invention by way of illustration, many modifications will occur to those skilled in the art. Therefore, I contemplate by the concluding claims to cover all such modiiications as fall within the true spirit and'scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1'. In the contact structure of an electric circuit breaker:

(a) movable and relatively stationary contact members adapted to conduct current in an electric power circuit;

(b) means for supporting said movable contact member in cooperative relationship with the relatively stationary contact member;

(c) means coupled to said movable contact member for moving the movable contact member between open and closed circuit positions;

(d) one of said contact members comprising at least one pair of electrically parallel arms disposed in side by side spaced-apart relation to each other, each of said arms having a free end and'each carrying in the vicinity of its free end both a butt contact surface and a slide contact surface, the slide contact surfaces of the respective arms being disposed facing one another;

(e) the other of said contact members including electrically interconnected butt contact surfaces positioned for abutting engagement with the respective butt contact surfaces of said arms whenever said movable member is in said closed circuit position;

(f) said other contact member further including a rigid part having a pair of slide contact surfaces on opposite sides thereof, said part being disposed in between said arms whenever said movable member is in its closed circuit position, with the slide surfaces of said part being adjacent to the slide surfaces of said arms, respectively, and being adapted to be separably engaged thereby; and

(g) saidother contact member also including means for electrically interconnecting its slide contact surfaces and its butt contact surfaces;

(h) said rigid part and said parallel arms being so constructed and arranged that the slide surface of each arm does not touch the associated slide surface of said part on movement of the movable member to said closed circuit position until said members conduct more than a predetermined amount of current.

2. In the contact structure of an electric circuit breaker:

(a) movable and relatively stationary contact members adaptedtto conduct current in an electric power circuit;

(b) means for supporting said movable contact member in cooperative relationship with the relatively stationary contact member;

(c) means coupled to said movable contact member for moving the movable contact member between open and closed circuit positions;

(d) said movable contact member comprising at least a pair of electrically parallel arms disposed in side by side spaced-apart relation to each other, said arms having corresponding free ends jointly movable in parallel planes upon movement of the movable contact member from open to closed circuit positions, each of said arms carrying in the vicinity of its free end a first contact surface generally transverse to its plane of movement and a second contact surface generally parallel to its plane of movement, the secondsurfaces of the respective arms being disposed facing one another; and

(c) said relatively stationary contact member comprising electrically interconnected yieldably supported 13 elements having contact surfaces positioned for abutting engagement, respectively, with the first contact surfaces of said arms whenever said movable member is in said closed circuit position and additionally comprising a protubera'rit part having at least a pair of slide contact surfaces on opposite sides thereof, said protuberant part being electrically connected to said elements and being mechanically supported so as to project inbetween said arms when the movable contact member is in its closed circuit position, with said slide surfaces being respectively adjacent to the second surfaces of said arms and being adapted to be separably engaged thereby.

3. An electric circuit breaker comprising: (a) first and second separable main contact means adapted when engaged to conduct current in an electric power circuit;

(b) two separable arcing contact means connected respectively to said first and second main contact means;

(c) operating means coupled to said contact means for moving the first main contact means into and out of circuit making engagement with the second main contact means and, concurrently, for moving one of said arcing contact rrieans toward and away from a position of proximity to the other arcing contact means, the two arcing contact means remaining separated during movement of said first main contact means into engagement with the second main contact means; and I (d) means associated with said contact means and responsive to the magnitude of current conducted by the main contact means for directly effecting the interengagement of the two arcing contact means,

said interengagement being effected independently of operation of said operating means;

(e) said arcing contact means being arranged to separate after the first and second main contact means have separated on operation of said operating means, while the two arcing contact means are interengaged, to move said first main contact means out of engagement with the second main contact means.

4. An electric circuit breaker comprising:

(a) first and second separable main contact means adapted when engaged to conduct current in an electric power circuit; I

(b) two separable arcing contact means electrically connected to said first and second main contact means, respectively, and adapted when engaged to shunt said first and second main contact means;

(c) operating means coupled to said contact means for moving the first main contact means into and out of circuit making engagement with the second main contact means and, concurrently, (for moving one of said arcing contact means toward and away from a position of proximity to the other arcing contact means, the two arcing contact means remaining separated during movement of said first main contact means into engagement with the second main contact means;

(d) said arcing contact means having associated therewith first means responsive to the magnitude of current conducted by the first and second main contact means for directly effecting the interengagement of the two arcing contact means, said interengagement being effected independently of operation of said operating means; and

(e) said arcing contact means also having associated therewith additional means for augmenting contact pressure therebetween in response to the conduction of current by the interengaged arcing contact means; (if) said arcing contact means being arranged to separate after the first and second main contact means have separated on operation of said operating means, while the two arcing contact means are interengaged,

14 to move said first main contact means out of engagement with the second main contact means.

5. In the contact structure of an electric circuit breaker:

(a) movable and relatively stationary contact members adapted to conduct current in an electric power circuit;

(b) first means for supporting said movable contact member in cooperative relationship with the relav tively stationary contact member;

(c) second means coupled to said movable contact member for moving the movable contact member from a closed circuit position to an open circuit position;

(d) third means coupled to said second means for actuating said second means in response to the conduction of short circuit current by said contact members;

(e) one of said contact members comprising a pair of electrically parallel arms disposed in side by side spaced-apart relation to each other, each of said arms having a free end and each carrying in the vicinity of its free end both a butt contact surface and a slide contact surface, the slide contact surfaces of the respective arms being disposed facing one another; and I v (-f) the other of said contact members including a pair of electrically interconnected butt contact surfaces positioned for abutting engagement with the respective butt contact surfaces of said arms whenever said movable member is in said closed circuit position;

(lg) said other contact member further including a protuberant part having a pair of slide contact surfaces on opposite sides thereof, said protuber'ant part being positioned to project inbetween said arms when said movable member is in its closed circuit position, with the slide surfaces of said part being adjacent to the slide surfaces of said arms, respectively, and being adapted to be separa'bly engaged thereby, the slide surfaces and the butt contact surfaces of said other contact member being electrically inter- I connected;

(h) said protuberant part and said arms being so constructed and arranged that the slide surfaces of said arms are separated from the respectively adjacent slide surfaces of said part when said other contact member is not conducting current and are moved into engagement with said adjacent surfaces, before said second means moves said movable contact member, by forces of attraction acting on said arms in response tosaid other member conducting current of more than a predetermined amount.

6. The contact structure of claim- 5 in which said movable and relatively stationary contact members are so constructed and arranged that the interengaging butt contact surfacesbecome disengaged, during movement of the movable member by said second means in response to said members conducting short circuit current of more than said predetermined amount, before the slide surfaces of said arms disengage the respectively adjacent slide surfaces of said protuberant part.

7. In the contact structure of an electric circuit breaker:

(a) movable and relatively stationary contact members adapted to conduct current in an electric power circuit;

(b) means connected to the contact members for supporting said movable contact member in cooperative relationship with the relatively' stationary contact member and for moving the movable contact memher from open to closed circuit positions with respect thereto;

(c) one to said contact members including a pair of electrically parallel laterally movable arms disposed in side by side spaced-apart relation to each other, each of said arms having a free end and each carrying in the vicinity of its free end both a butt contact surface and a slide contact surface, the slide contact surfaces of the respective arms being disposed facing one another, and said one contact member further including means for yieldably maintaining a predetermined spacing between said slide contact surfaces whenever said movable member is in said open circuit position;

((1) the other of said contact members including a pair of electrically interconnected butt contact surfaces positioned for abutting engagement with the butt contact surfaces of said arms, respectively, at the conclusion of the closing movement of said movable member;

(e) said other contact member further including a part having a pair of slide contact surfaces generally parallel to the slide surfaces of saidarms, respectively, said part projecting in the space between said arms with its slide surfaces respectively adjacent to but not being touched by the facing slide surfaces of the arms when said butt contact surfaces initially engage as the movable member approaches its closed circuit position near the conclusion of said closing movement, the slide surfaces of said arms respectively engaging the adjacent slide surfaces of said part upon lateral movement of said arms toward one another while said butt surfaces are interengaged; and

(f) means for electrically connecting the butt contact surfaces of said other contact member to the slide contact surfaces of said part.

8. In the contact structure of an electric circuit breaker:

(a) a base member;

(b) an electroconductive supporting bracket mounted on the base member;

(c) a pair of jointly movable electroconductive arms pivotally connected to the bracket in side by side spaced-apart relation to each other, each of said arms having a free end disposed for major movement along a predetermined arcuate path and each arm carrying in the vicinity of its free end a first contact surface generally transverse its path of major movement and a second contact surface generally parallel to a plane defined by said path, the second surfaces of the respective arms being disposed facing one another;

(d) the connection between the supporting bracket and each of said arms including contiguous slide surfaces disposed generally parallel to said plane to form a current-conducting joint, one of said slide surfaces being substantially flat and the other being raised so that the contiguous portions thereof provide a fulcrum oriented at approximately a right angle with respect to the longitudinal centerline of the arm for lateral rocking movement by the arm in a direction generally perpendicular to said plane;

(e) actuating means-coupled to said arms and movable between predetermined positions with respect to the base member for moving the free ends of both arms in parallel relationship along their respective paths or major movement;

(f) resilient means associated with both of said arms for yieldably opposing their lateral movement in a direction toward one another, thereby tending to maintain a predetermined spacing between the second contact surfaces of the respective arms; and

(g) a relatively stationary contact member mounted on the base member in spaced relation to the bracket,

the relatively stationary contact member comprising (i) main contact surfaces positioned for abutting engagement by the first contact surfaces of the respective arms when said actuating means is in a first one of its predetermined positions, and Y r faces and are adapted to be separab'ly engaged 7 thereby.

9. In an electric circuit breaker:

(a) a base member;

(b) a relatively stationary contact. member mounted on the base member and including (i) a pair of opposing contact fingers disposed for relatively limited pivotal movement in a common plane, opposing ends of said fingers having complementary contact surfaces, respectively, and

(ii) a protuberant part having parallel slide contact surfaces on opposite sides thereof, said slide surfaces being substantially perpendicular to said common plane and also being substantially perpendicular to said complementary surfaces;

(c) a bracket mounted on the base member in spaced relation to the stationary contact member;

(d) a pair of electrically parallel contact arms pivotally connected to the bracket and having corresponding free ends respectively disposed for arcuate movement in generally parallel planes that are substantially perpendicular to said common plane and to said complementary surfaces, the arms having in the vicinity of their respective free ends (i) transverse contact surfaces disposed in abutting relation to the complementary surfaces of said fingers, respectively, and

(ii) additional slide contact surfaces paralleling said parallel planes and facing one another, said additional surfaces being disposed respectively adjacent to the opposite slide surfaces of said protuberant part whenever said transverse surfaces are in engagement with the respective complementary surfaces of the fingers; and

(e) actuating means coupled to said arms for jointly moving the transverse surfaces thereof into and out of engagement with said complementary surfaces.

10. In an electric circuit breaker:

(a) a base member;

(b) a relatively stationary contact member mounted on the base member comprising (i) two adjacent pairs of opposing contact elements, the opposing ends of the elements of each pair being respectively provided with complementary contact surfaces disposed in a common plane, and

(ii) a protuberant part having slide contact surfaces on opposite sides thereof, said slide surfaces being generally parallel to and on opposite sides of a bisector of said opposing elements and also being substantially perpendicular to said common plane;

(c) a bracket mounted on the base member in spaced relation to the stationarycontact member;

((1) a movable contact member pivotally connected to the bracket comprising a pair of arms having corresponding ends respectively disposed for joint arcuate movement between open and closed circuit positions in generally parallel planes paralleling the slide surfaces of said protuberant part, each of the corresponding ends of said arms being provided with (i) at least one transverse contact surface disposed in cooperative relationship with the contact surfaces of adjacent contact elements of said pairs for substantially simultaneously engaging the same during a circuit closing operation of the circuit breaker, and,

(ii) a slide contact surface generally parallel to its plane of movement, the respective slide surfaces of said ends being disposed adjacent to and being adapted to separably engage the respective slide surfaces of said protuberant part whenever the associated transverse surfaces are in engagement with the contact surfaces of said elements; and

(e) actuating means coupled to the movable contact member for jointly moving said arms.

11. In the contact structure of an electric circuit breaker:

(a) movable and relatively stationary separable contact members;

(b) means for supporting said movable contact member in cooperative relationship with the relatively stationary contact member;

(c) means coupled to said movable contact member for reciprocating the movable contact member between predetermined open and closed circuit positions to obtain breaker closing and opening operations, respectively;

(d) said movable contact member comprising a pair of electrically parallel electroconductive arms disposed in side by side spaced-apart relation to each other, said arms having corresponding free ends jointly movable in parallel planes on movement of the movable contact member from open to closed circuit positions, each of said arms carrying in the vicinity of its free end a first contact surface generally transverse the plane of movement of its free end and each of said free ends being terminated by a contact tip having a second contact surface generally parallel to its plane of movement, the second surfaces of the respective arms being disposed facing one another;

(e) said relatively stationary contact member comprising (i) a pair of electrically interconnected yieldably supported elements having contact surfaces positioned for abutting engagement, respectively,

by the first contact surfaces of said arms during a breaker closing operation and (ii) a protuberant part having a pair of slide con tact surfaces on opposite sides thereof, said protuberant part being electrically connected to said elements and being mechanically supported so as to project inbetween the contact tips of said arms when the movable contact member is in its closed circuit position, with said slide surfaces then being respectively disposed adjacent to the second surfaces of said arms for engagement thereby on movement of said contact tips toward one another in response to conduction by the arms of more than a predetermined amount of electric current;

(f) said movable and relatively stationary cogitact members being so constructed and arranged that the second surfaces are still respectively adjacent to said slide surfaces when the first contact surfaces disengage the contact surfaces on said elements during a subsequent breaker opening operation; and

(g) means enclosing said contact tips and said protuberant part for extinguishing any electric arc extending therebetween during the breaker opening operation.

18 12. In the contact structure of an electric circuit breaker:

(a) movable and relatively stationary contact members adapted to conduct current in an electric power circuit;

( b) first and second mounting means for supporting said movable and relatively stationary contact members, respectively;

(c) said movable contact member comprising a pair of electroconductive arms supported at one end on said first mounting means and disposed in side by side spaced-apart relation to each other for joint -movement in parallel planes between two dilferent positions, each of said arms being adapted to be connected at said one end to a common point of the electric circuit and each arm having a main contact surface generally transverse its plane of movement, said arms having at corresponding free ends thereof additional contact surfaces generally parallel to their respective planes of movement, with the additional surfaces being disposed facing one another;

(d) means coupled to said arms for jointly moving them between said two different positions; and

(c) said relatively stationary contact member comprising (i) main contact surfaces adapted to be connected to another point of the electric circuit and positioned on said second mounting means for abutting engagement by the transverse surfaces of the respective arms of the movable member when the arms are in a predetermined one of said positions,

(ii) an electroconductive part supported by said second means so as to project inbetween the free ends of said arms when the arms are in said predetermined position, said part having on opposite sides thereof a pair of arcing contact surfaces disposed respectively adjacent to and adapted to be separably engaged by said additional surfaces of the free ends of said arms, and

(iii) a pair of electrically parallel stationary conductors connected between said main contact surfaces and said projecting part of the relatively stationary contact member, said conductors being respectively located on opposite sides of and in alignment with said arms when said arms are in said predetermined position.

References Cited by the Examiner UNITED STATES PATENTS 2,761,040 8/1956 Ulrich 200-146 2,938,986 5/ 1960 Baskerville et al. 200164 References Cited by the Applicant UNITED STATES PATENTS 1,748,724 2/ 1930 Morger. 1,762,604 6/ 1930 Ainsworth. 1,958,159 5/1934 Bresson. 2,567,606 9/ 1 Kojis. 2,821,594 1/ 1958 Latour. 2,918,552 12/ 1959 Fust.

KATHLEEN H. CLAFFY, Primary Examiner.

H. O. JONES, Assistant Examiner. 

1. IN THE CONTACT STRUCTURE OF AN ELECTRIC CIRCUIT BREAKER: (A) MOVABLE AND RELATIVELY STATIONARY CONTACT MEMBERS ADAPTED TO CONDUCT CURRENT IN AN ELECTRIC POWER CIRCUIT; (B) MEANS FOR SUPPORTING SAID MOVABLE CONTACT MEMBER IN COOPERATIVE RELATIONSHIP WITH THE RELATIVELY STATIONARY CONTACT MEMBER; (C) MEANS COUPLED TO SAID MOVABLE CONTACT MEMBER FOR MOVING THE MOVABLE CONTACT MEMBER BETWEEN OPEN AND CLOSED CIRCUIT POSITIONS; (D) ONE OF SAID CONTACT MEMBERS COMPRISING AT LEAST ONE PAIR OF ELECTRICALLY PARALLEL ARMS DISPOSED IN SIDE BY SAID SPACED-APART RELATION TO EACH OTHER, EACH OF SAID ARMS HAVING A FREE END EACH CARRYING IN THE VINCINITY OF ITS FREE END BOTH A BUTT CONTACT SURFACES AND A SLIDE CONTACT SURFACE, THE SLIDE CONTACT SURFACES OF THE RESPECTIVE ARMS BEING DISPOSED FACING ONE ANOTHER; (E) THE OTHER OF SAID CONTACT MEMBERS INCLUDING ELECTRICALLY INTERCONNECTED BUTT CONTACT SURFACES POSITIONED FOR ABUTTING ENGAGEMENT WITH THE RESPECTIVE BUTT CONTACT SURFACES OF SAID ARMS WHENEVER SAID MOVABLE MEMBER IS IN SAID CLOSED POSITION; (F) SAID OTHER CONTACT MEMBER FURTHER INCLUDING A RIGID PART HAVING A PAIR OF SLIDE CONTACT SURFACES ON OPPOSITE SIDES THEREOF, SAID PART BEING DISPOSED IN BETWEEN SAID ARMS WHENEVER SAID MOVABLE MEMBER IS IN ITS CLOSED CIRCUIT POSITION, WITH THE SLIDE SURFACES OF SAID PART BEING ADJACENT TO THE SLIDE SURFACES OF SAID ARMS, RESPECTIVELY, AND BEING ADAPTED TO BE SEPARABLY ENGAGED THEREBY; AND (G) SAID OTHER CONTACT MEMBER ALSO INCLUDING MEANS FOR ELECTRICALLY INTERCONNECTING ITS SLIDE CONTACT SURFACES AND ITS ABUTT CONTACT SURFACES; (H) SAID RIGID PART AND SAID PARALLEL ARMS BEING SO CONSTRUCTED AND ARRANGED THAT THE SLIDE SURFACE OF EACH ARM DIES NOT TOUCH THE ASSOCIATED SLIDE SURFACE OF SAID PART ON MOVEMENT OF THE MOVABLE MEMBER TO SAID CLOSED CIRCUIT POSITION UNTIL SAID MEMBERS CONDUCT MORE THAN A PREDETERMINED AMOUNT OF CURRENT. 